Plant, Property, and Equipment (Public Utilities Property Plant and Equipment Schedule of Accumulated Depreciation and Amortization) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accumulated Depreciation, Depletion and Amortization	$ 4,901	$ 4,646
Consumers Energy Company [Member]
Accumulated Depreciation, Depletion and Amortization	4,846	4,593
Utility Plant Assets [Member]
Accumulated Depreciation, Depletion and Amortization	4,844	4,592
Utility Plant Assets [Member] | Consumers Energy Company [Member]
Accumulated Depreciation, Depletion and Amortization	4,844	4,592
Non-Utility Plant Assets [Member]
Accumulated Depreciation, Depletion and Amortization	57	54
Non-Utility Plant Assets [Member] | Consumers Energy Company [Member]
Accumulated Depreciation, Depletion and Amortization	$ 2	$ 1